Control of vaporizable material



W. S. FROHOCK CONTROL OF VAPORIZABLE MATERIAL Filed Nov. 20. 1945 C INVENTOR Fkohag a WW 5.

ATTORNEY Patented Dec. 14, 1948 CONTROL OF VAPORJZABLE MATERIAL Warren S. Frohock, Danvers, Masa, assignor to Sylvania Electric Products Inc., a corporation of Massachusetts Salem, Masa,

Application November 20, 1945, Serial No. 829,848

2 Claims. 1

This invention relates to the measurement and control of vapors, and particularly to the measurement and control of the amount or a' condensible material, such as mercury, present in an electric discharge lamp.

The quantity of mercury present in a fluorescent lamp, for example, must be above a certain value to prevent its beingused up early in the life of the lamp, thereby reducing the latter's brightness. n the other hand, the quantity should not be too large, for that would increase the cost of the lamp and reduce its brightness because of the absorbtion of light by the excess mercury condensed on the bulb or in the fluorescent coating.

It is thus important to know that each lamp manufactured has its proper amount of mercury in it. Sometimes the mercury dispensing devices fail to introduce the proper amount. Photoelectric devices have been proposed to determine this, but they have merely detected the presence or absence of mercury in the lamp, and did not determine whether its quantity is correct.

I have found that the quantity of mercury in the lamp can be quickly and accurately determined by heating the lamp during manufacture to a temperature suillclent to vaporize, all, or most of, the mercury and measuring the voltage across the lamp in that condition. The voltage will depend on the amount of mercury vaporized, and hence on the amount in the lamp. Fluorescent and other discharge lamps are ordinarily baked at a high temperature, anyway, during manufacture and the measurement can thus be easily made. If the amount of mercury is insufficient the voltage will be excessive, and .this excess in voltage can be used to cause more mercury to be introduced into the lamp, by means of relays,-ii desired.

The invention will be further understood from the following specification and its accompanying drawings.

Fig. 1 is a schematic diagram of one embodiment of the invention; and

Fig. 2 is a curve of lamp voltage against, mercury content while the lamp is heated on exhaust. v In Fig. 1, the by the glass stems 2 and 3, through which lead-in wires 4, 5, 8, I extend, which are connected to the electrodes 8, 9, which may be tungsten wire coils coated with one or more of the alkaline earth oxides. An exhaust tube l0 extends from the stem 8, to which it is sealed in the usual manner to the exhaust head ll, through which the lamp is exhausted in the usual manner. This head plates 13, it, ill,

glass lamp envelope I is closed terminals, and the may have a mercury dispenser, 3| (not fully shown) in register with it, for example as shown in U. 8. Patents 2,247,513 issued July 1, 1941 to A. J. Marshaus or 1,860,106 issued May 24, 1943 to LeVan. The dispmser may be magnetically controlled by a wire cell I! in the manner of that patent. r

The lead-in wires 4, 5, 8, I contact the metal I6 for example as shown in U. 8. Patent 2,313,788 issued March 16, 1943 to Walter H. Van Dyke.

The lamp is exhausted in the usual manner and filled with an inert gas at low pressure. this process is it heated in an oven, for example, as shown in U. S. Patents 2,294,400 to Gardner et al. and 2,334,718 to E. F. Lowry et al. Heating 01 the lamp may be accomplished by using resistance heating elements 40, for example, which are connected to a source of electrical energy such as the lines 29 and 82. At some stage of the process, mercury is dispensed into the lamp through the exhaust tube iii. If the dispenser fails, or if insuillcient mercury gets into the lamp, my invention will come into action.

After the bulb is heated to a temperature sufflcient-to the mercury, which temperature may be, for example C. for the usual 40 watt fluorescent lamp. a voltmeter may be placed across its mercury content determined by the voltage across the lamp. The voltage will be high say 200 volts with the lamp mentioned, for very small mercury content, and much lower say '70 volts for larger mercury contents.

Thus if the mercury content desired is 15 mg. the corresponding voltage will be 83 volts, and the relays in the circuit of Fig. 1 will be set so that they do not actuate the mercury dispenser to add mercury to the tube unless the voltage is above .83 volts. This is done by throwing the 4 P. D. T.

toggle switch 18 to the calibrating position and adjusting the "Variac (variable transformer) 30 to give a reading of 83 volts on meter V. The rheostat I8 is adjusted for maximum resistance and then its resistance is reduced until the signal lamp 211, in shunt to the dispenser coil l2, lights. The apparatus then being calibrated, or set for 83 volts; that is 83 volts or more will operate the relay and dispenses additional mercury into the thi The switch it is then thrown to the operating position, which connects wires 2i and 22, from opposite electrodes 8. 9 of the lamp to the high impedance relay 23, through resistor is and mercury switch 24, of any usual type. When the During lamp. Anything less than 83 volts will not do relay or' contactor' mercury switch is closed, for an instant, for example, by the indexing mechanism of the exhaust machine, the relay will operate if the voltage across it is 83 volts or more. (In the calibrating position. the mercury switch is shorted by the switch IS.) The operation of the high impedance relay 23 closes the contacts 25, 28 of the power 21 by shorting the armature 28 across them, and thus supplies power to actuate the dispenser coil i2 from the 115 volt A. C. lines 29, 32. from this same line, if desired, but the Variac? 30 may generally be operated from a 230 v. A. C. line, for convenience, such as it, 34.

Voltages lower than 83 volts will not actuate the relays. and hence will not add further mercury to the lamp. Large excesses of mercury, say up to 80 mg. will not vary the voltage much, although when suflicient excess is available to produce a very high pressure the voltage may rise. Since the dispenser puts only a small fixed quantity into the lamp at a, time, the excess will never be great.

The value of 83 volts was chosen merely by way of example, and not by way of limitation.

The lamp should be raised to a temperature suilicient to just vaporize completely the minimum amount of mercury desired in the lamp. Under this condition, the excess mercury present above the desired value will not be vaporized and will not affect the voltage. In Fig. 2, for example, the voltage is substantially constant between 20 and 80 milligrams of mercury. For example, a tsmperature of 115 C. is used by us in fluorescent lamp work. It the lamp temperature is too far above the desired point, the discharge may hecome a high pressure arc'and cause a rise in voltage after the initial drop, if a considerable excess of mercury is present. Then, if more than this is present, the voltage will be too low to actuate the relay and add more mercury. while if it is less, the relays will be actuated and more mercury added.

An inert gas at a pressure of a few millimeters The power" relay may also operate of mercury was present in the lamps corresponding to the curve of Fig. 2. This was in addition to the mercury vapor.

What I claim is:

1. Apparatus for insuring that at least a determined amount of mercury is present in a low. pressure discharge lamp having two electrodes said apparatus comprising: means for heating said lamp to a temperature suiilcient to vaporize the determined amount of mercury, means for passing current through the resultant vapor to produce a voltage between said electrodes, and means directly responsive to the voltage between said electrodes for adding more mercury to the lamp if said voltage is below a determined value corresponding to the determined amount of mer- W.

2. Apparatus for insuring that at least a determined amount of mercury is present in a low pressure discharge lamp having two electrodes, said apparatus comprising: means for heating said lamp to a temperature suflicient to vaporize the determined amount of mercury, means for passing current through the resultant vapor to produce a voltage between said electrodes, a relay connected between said electrodes for actuation when the voltage between said electrodes rises above a pre-determined value, and a mercury dispenser controlled by the actuation of said relay for adding more mercury to the lamp if said voltage is above a determined value corresponding to the determined amount of mercury.

WARREN S. FROHOCK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,697,339 Baker Jan. 1, 1929 2,211,930 Chirelstein Feb. 23, 1943 2, 74,304 Owings Apr. 24, 1945 2,417,361 Herzog Mar. 11, 1947 

